Pyridylpropyl cyclohexene carboxylates as insect repellents

ABSTRACT

Compounds having the formula   &lt;IMAGE&gt;   in which R is hydrogen or C1-C4 alkyl are insect repellents.

This invention relates to compounds having the formula ##STR2## in which R is hydrogen or C₁ -C₄ alkyl. Preferably R is hydrogen or methyl.

As will be shown from the data which follows, these compounds have been found to have utility in repelling insects, particularly repelling flying insects, and most particularly houseflies, from lighting and/or feeding.

In the compounds, the side chain may be attached to the pyridine ring at the 2-, 3- or 4-position. Similarly, the carboxylate group may be attached to the cyclohexene ring at the 1-, 2- or 3-position.

The compounds of this type can be prepared by reaction of an appropriate pyridyl propanol with a cyclohexene carbonyl halide (preferably chloride) according to the reaction ##STR3##

The pyridyl propanols in which R is C₁ -C₄ alkyl, if not commercially available, can be synthesized for example by the method of Umezawa et al., Japanese Patent Application No. 74/13180.

The reaction to produce the desired compounds is generally conducted at temperatures of from about 0° C. to about 25° C. in the presence of a solvent such as methylene chloride, or other suitable inert solvent and a hydrogen halide acceptor such as sodium bicarbonate, or a tertiary amine such as triethylamine or pyridine. The product is recovered by conventional extraction, washing, filtration, and other purification steps as may be necessary. Optionally, the hydrogen halide acceptor may be added after the reaction has gone to completion.

The preparation of these compounds is illustrated by the following example.

EXAMPLE 1 Preparation of 3-(3-Pyridyl)-1-propyl-1-cyclohexenecarboxylate (Compound No. 1 herein)

In a flask were placed 4.3 grams (g) (0.031 mole) of 3-(3-pyridyl)-1-propanol, 2.5 g of pyridine and 50 milliliters (ml) methylene chloride. The clear yellow solution was cooled to 0° C. with an ice bath; then there was added 4.5 g (0.031 mole) of 1-cyclohexene carbonyl chloride at a rate so as to maintain the temperature of the mixture at 15° C. maximum. After addition was complete, the reaction mixture was warmed to room temperature and allowed to stir for one hour.

After that, the mixture was washed with water, saturated aqueous sodium carbonate, water again and saturated aqueous sodium chloride, filtered through sodium sulfate and dried under vacuum. A clear yellow, viscous oil was obtained as a crude product. This was purified by low pressure liquid chromatography on silica gel with elution by 50:50 hexene: ethyl acetate to produce 4.4 g (57% of theoretical yield) of the desired product, a clear, yellow oil, n_(D) ³⁰ 1.5191. The structure of the product was confirmed by infrared, nuclear magnetic resonance, and mass spectroscopy.

The following Table I contains a list of representative compounds of this invention which were prepared by the above process, and whose structure was similarly confirmed by analyses.

                  TABLE I                                                          ______________________________________                                          ##STR4##                                                                      Compound       Position On                                                                               Position on                                          Number  R      Pyridine Ring                                                                             Cyclohexene Ring                                                                          n.sub.D.sup.30                            ______________________________________                                         1       H      3-         1-         1.5191                                    2       H      4-         1-         1.5197                                    3       CH.sub.3                                                                              2-         1-         1.5218                                    4       H      2-         1-         1.5234                                    5       H      3-         3-         1.5176                                    ______________________________________                                    

INSECT REPELLENCY TESTS

The compounds described in Table I above were tested for insect repellency by the following procedures:

Houseflies:

The insect utilized for this test was the housefly, Musca domestica (L.). One hundred houseflies of mixed sexes were placed in test cages. In each cage was placed a sugar cube saturated with 1.0 ml of acetone containing 0.1% (by weight) of the test compound. The cube was dried and weighed before being placed in the cage. Each cage also contained a water-saturated cotton plug to provide moisture. The test cages were placed on a turntable and rotated at 1.5 revolutions per minute to keep the flies randomly distrubuted inside the cage. After 48 hours the flies in each cage were anesthetized with carbon dioxide. The sugar cubes were removed and reweighed and the percentage weight loss (due to consumption by the flies) recorded. A repellency ratio, calculated as the percent weight loss of the treated sugar cube divided by the percent weight loss of a control sugar cube treated with only acetone and no test compound, was calculated. The lower the repellency ratio, the greater the repellency of the test compound. The repellency ratios of the test compound at different concentrations are shown in the following Table II.

Stable Fly; Yellow Fever Mosquito

Insects utilized for these tests were the stable fly, Stomoxys calcitrans and yellow fever mosquito, Aedes aegypti.

Pupae of these insects were placed in separate standard fly cages and allowed to emerge into adults. The mosquitoes were supplied with a sugar-water solution; the stable flies with water, sugar cubes, and casein. Tests on mosquitoes were performed at least 3 days after the adults emerged; those on stable flies, one day after emergence because of the short life span (4-5 days) of these flies without a blood meal.

Test compounds were weighed and dissolved in acetone. One milliliter (ml) of the test solution was pipetted onto a 9×9 cm swatch of cotton stocking. The swatches were then allowed to dry for 1 hour.

A square opening 6×6 cm was made in an upper corner of one side of each fly cage. A large, hard cardboard disk was placed over the opening so that it could be rotated to either cover or expose the opening as desired. One-half of the disc was left intact. In the remaining half, several 6×6 cm square openings were cut. When the intact half of this disc was located over the opening in the fly cage, this opening was effectively sealed.

Swatches of treated stocking were placed over the square holes in the disc and held in place by metal frames attached to magnetic tape.

To initiate the test, the disc was rotated so that a treated swatch became located over the opening in the cage. The palm of the tester's hand was placed over a cardboard ring, 8 cm in diameter and 1 cm thick. The ring acted as a spacer and protected the hand from bites which could otherwise be inflicted by the insects. A breath of air was exhaled through tubing into the opening, so that insects could be attracted to the swatch by the warm, moist air and the tester's hand. The number of insects landing on the swatch was observed, and the number probing was recorded during a 1-minute exposure. Repellency was considered to occur when 10 or fewer insects probed the swatch during the exposure.

The compounds were tested at the rate of 0.1 mg/cm² of swatch. The results of these tests on stable flies (SF) and yellow fever mosquitos (YFM) are contained in Table II.

                  TABLE II                                                         ______________________________________                                                 HF,        Number of Insects probing/min.                              Compound                                                                               Repellency 0.1 mg (m.sup.2)                                            Number  Ratio      SF             YFM                                          ______________________________________                                         1       0.42         9. >10, 7, 2*                                                                               >10                                          2       0.36       >10            >10                                          3       0.24       >10            >10                                          4       0.40       >10            4.1**                                        5       0.21       >10            >10                                          ______________________________________                                          *Results of 4 trials.                                                          **Average of 10 trials.                                                  

The novel compounds of this invention may be used as an insect repellent in either diluted or undiluted form. When used in a diluted form, compositions may contain relatively high or relatively low concentrations of the active compound. For example, the active compound can be incorporated into relatively high concentration compositions such as wet sprays or solutions in alcohol or other suitable solvents. Such compositions may contain, in addition to the active compound, adjuvants such as emulsifying agents, surface-active agents, anti-oxidants and propellants which may be normally found in insect repellent preparations. The active compound of this invention may be employed as the sole active component of such compositions or may be used in admixture with other compounds having a similar or different utility. For example, the compound may be incorporated into creams, lotions, powders, suntan oil, insecticides and other preparations which may contain pesticidal or other useful substances, as well as into compositions of various types for treating fabrics or articles of clothing to render them insect repellent. In general, compositions for repellent use may contain from 0.1 up to 95 weight%, preferably from 1 to about 40 weight%, of the novel compound. Hight concentration formulations, containing up to 95% of the compound, could also be utilized for low-volume spraying from the air.

Examples of typical formulations employing the compound of this invention are for instance,

EXAMPLE 1: EMULSIFIABLE CONCENTRATE

    ______________________________________                                         Component            Weight %                                                  ______________________________________                                         Compound 1           53.6                                                      Aromatic Hydrocarbon Solvent                                                                        36.4                                                      Emulsifier           10.0                                                      Total                100.0                                                     ______________________________________                                    

EXAMPLE 2: LOTION

    ______________________________________                                         Component           Weight %                                                   ______________________________________                                         Compound 2          10.7                                                       Lanolin             4.8                                                        Mineral Oil         8.0                                                        Trihydroxyethylamine stearate                                                                      1.8                                                        Glycosterin         0.8                                                        Glycerine           4.6                                                        Sodium Benzoate     1.0                                                        Water               68.3                                                       Total               100.0                                                      ______________________________________                                    

EXAMPLE 3: ALCOHOL SOLUTION

    ______________________________________                                         Component      Weight %                                                        ______________________________________                                         Compound 3     53.6                                                            Isopropanol    46.4                                                            Total          100.0                                                           ______________________________________                                    

EXAMPLE 4: ALCOHOL SOLUTION

    ______________________________________                                         Component      Weight %                                                        ______________________________________                                         Compound 4     80.0                                                            Ethanol        20.0                                                            Total          100.0                                                           ______________________________________                                    

EXAMPLE 5: WETTABLE POWDER

    ______________________________________                                         Component            Weight %                                                  ______________________________________                                         Compound 5           26.9                                                      Hydrated Calcium Silicate                                                                           62.1                                                      Sodium Lignosulfonate                                                                               5.0                                                       Orzan A (mixture of ammonium                                                                        5.0                                                       lignosulfonate and wood sugars)                                                Wetting Agent        1.0                                                       Total                100.0                                                     ______________________________________                                     

What is claimed is:
 1. A compound having the formula ##STR5## in which R is hydrogen or C₁ -C₄ alkyl.
 2. A compound according to claim 1 in which R is hydrogen, the side chain is substituted on the pyridine ring at the 3-position, and the carboxyl group is substituted on the cyclohexene ring at the 1-position.
 3. A compound according to claim 1 in which R is hydrogen, the side chain is substituted on the pyridine ring at the 4-position, and the carboxyl group is substituted on the cyclohexene ring at the 1-position.
 4. A compound according to claim 1 in which R is methyl, the side chain is substituted on the pyridine ring at the 2-position, and the carboxyl group is substituted on the cyclohexene ring at the 1-position.
 5. A compound according to claim 1 in which R is hydrogen, the side chain is substituted on the pyridine ring at the 2-position, and the carboxyl group is substituted on the cyclohexene ring at the 1-position.
 6. A compound according to claim 1 in which R is hydrogen, the side chain is substituted on the pyridine ring at the 3-position, and the carboxyl group is substituted on the cyclohexene ring at the 3-position.
 7. A method for repelling insects comprising applying to a locus to be protected from insects an amount of a compound according to claim 1, effective to repel insects from said locus.
 8. A method according to claim 7 in which the insect is the housefly.
 9. An insect repelling composition containing an amount of a compound according to claim 1 effective to repel insects from lighting or feeding, and an inert diluent or carrier suitable for insect repellent compositions. 